To prevent the melting of a motor coil.

The temperature of a motor coil 62A rises when feeding of power supply is continued. When the temperature rises, the resistance value increases, and current passing through the motor coil 62A becomes small. The voltage applied to a resistor 155 decreases, corresponding to the current value flowing through the motor coil 62A. A comparison part 152 compares a voltage value V of the resistor 155 with a prescribed value of threshold A. Using the comparison results from the comparison part 152, a control part 153 controls the turning-on and -off of a transistor 154. By the turning on and off the transistor 154, the current passing through the motor coil 62A is controlled so as not to exceed the prescribed temperature.